The present invention relates to improvements in a filter for tobacco smoke.
It is widely known that tobacco smoke contains toxic and mutagenic components which are harmful to smokers. Conventional cellulose acetate filters, with or without additional activated charcoal, are ineffective in reducing the capacity of cigarette smoke to elicit mitotic abnormalities in test systems, when compared to unfiltered cigarettes (Sabharwal PS et al., Mutat Res, 1975 1:217-24). Since conventional filters provide little protection, there exists a need to provide filters with the capacity to reduce the amounts of cytotoxic materials in cigarette smoke.
There have been many attempts over many years to develop cigarette filters which can reduce the toxicity of tobacco smoke. A variety of filter compositions and additives have been suggested for selective removal of particular classes of toxic smoke components.
A strategy for improving the efficacy of tobacco smoke filters is wet filtration, in which a moistened filter (generally in a plastic holder in which a cigarette is inserted) is used to reduce smoke toxicity. The water increases the capacity of the filter to remove smoke components during passage. For example, there is presently on the market a product called "Aqua Filter" which comprises a cigarette holder containing a filter or cartridge which is prewet with a fluid containing water. In order that the fluid or water will not evaporate between the time of manufacture and the time of use, the reservoir, container or cigarette holder having the filter therein has its ends sealed by an insert at the cigarette end and a plastic top at the mouthpiece end. These parts must be removed at the time the holder is used for the smoking of a cigarette. Also, the manufacturer recognizes that the seal provided at each end of the holder may not be effective, and it is suggested that if some of the moisture has evaporated when the product is ready for use, the filter insert may be re-moistened by putting the large end under a faucet. It is apparent that it is essential to provide suitable means for sealing in order not to lose the fluid or moisture by evaporation or otherwise. The provision of the sealing means increase the cost of the parts and the cost of assembling the parts with the cigarette holder.
Glycerol has been proposed for use as wetting agents to improve smoke filtration (U.S. Pat. No. 3,674,540). Glycerol is a liquid, however, which hinders its commercial use in conventional paper-encased filters in amounts sufficient to significantly improve retention of smoke components in filters.
Another approach has been to incorporate water/methylated silica complexes into filter material, where the complexes break down under the heat of smoke passing through the filter to liberate water, which then moistens the filter material (U.S. Pat. No. 4,076,031). The feasibility of this approach, however, is contingent upon the stability of the silica-water complex.
Another approach to wet filtration has been a proposal to incorporate a liquid-containing module in the filter, which module can be ruptured mechanically by the smoker to release moisture into the filter (Japanese Patent Document 62022583-A).
In view of the prior art, there is a need for an efficient wet filtration system for tobacco smoke, which can be used with existing filter materials, but does not break down during heat, does not create health problems, is dependable, and is convenient to use.